The present invention relates to a flooring material for building and, more particularly, it relates to a flooring material which can be installed with high precision by simply placing it on a flat subfloor such as a wood subfloor composed of plywood or particle board, a concrete subfloor composed of RC, or an OA floor, without using an adhesive,
Among conventional flooring materials to be installed on subfloors, a material consisting of a solid or multi-ply floorboard and of a fiber mat or cushion sheet is well known. In the conventional flooring material, the fiber mat or cushion sheet is attached to the back face of the solid or multi-ply floorboard, serving as the base board, in order to improve its sound insulation. This type of floorboard is attached onto a subfloor by means of an adhesive. In this case, however, since the base board composing the flooring material has large rigidity and hence is inferior in flexibility, the fitting condition between the flooring material and subfloor also becomes inferior if the flooring material is installed on an uneven subfloor. Moreover, the adhesive must be applied in the execution of flooring. Furthermore, the renewal of the flooring material will be difficult since it is attached to the subfloor by means of the adhesive.
To overcome the difficulties, a flooring material shown in FIGS. 4 and 5 has been proposed. The flooring material is imparted with flexibility by forming a plurality of nick grooves B in the back face of a wood overlaid base board A in the shape of a rectangle having an overlay material thereon. The nick grooves B are spaced at proper intervals in the longitudinal direction of the base board A and extend in the lateral direction of the base board A while penetrating it. On the back face of the wood overlaid board A is integrally layered a thin elastic sheet C. For the purpose of joining adjacent pieces of the flooring material together, one longitudinal side face of the wood overlaid board A is formed with a tongue D, while the other longitudinal side face thereof is formed with a groove E.
Although the flooring material can be installed on the subfloor without using an adhesive or nails, it has the following disadvantage in the case where the surface of the subfloor is slightly curved. That is, though the wood overlaid board A is formed with a large number of nick grooves B at its lower portion, the flooring material spreads only in the horizontal direction due to its rigidity. The flooring material can be fitted to the surface of the subfloor only by the application of an external force. However, even if the external force applied makes the flooring material fit the surface of the subfloor, the flooring material will lift up from the subfloor by resilience when the external force is removed. This not only impairs the outward appearance of the finished floor but also causes a squeaking-floor phenomenon when a person walks on the floor.
Such a disadvantage can be prevented by increasing the depth of the nick groove B. However, if the depth of the nick groove B is increased, the overall strength of the flooring material is decreased, resulting in the breakage of the wood overlaid board A or in the rupture of the elastic sheet C placed on the back face of the wood overlaid board A due to its own expansion and contraction.
Moreover, if the wood overlaid board A is warped or distorted, the elastic sheet C placed on the back face thereof is also deformed in accordance with the warp or distortion of the wood overlaid board A. Therefore, it becomes difficult to keep the elastic sheet C in contact with the entire surface of the subfloor, though the elastic sheet C is provided so as to absorb the unevenness of the subfloor. Consequently, spaces are generated in places between the flooring material and the subfloor, which may cause the squeaking of the floor mentioned above or generate a difference in level or space at the joint of adjacent pieces of the flooring material, so that the flooring material cannot be installed with high precision.
Furthermore, since the tongue D is provided in one side face of the wood overlaid board A, if the depth of the nick groove B is increased, the tongue D is completely divided into a large number of pieces d by the nick grooves B. Consequently, there are cases in which the tongues D are broken during carriage or execution, so that not only the market value of the flooring material is lowered but also a strong joint cannot be obtained between adjacent pieces of the flooring material when they are joined together by fitting the tongues D into the groove E. To solve the problem, a reinforcing sheet may be attached to the tongues D over the top or back faces thereof. However, this not only adds extra labor to the fabrication process but also causes the following problem. That is, the reinforcing sheet decreases the flexibility of the flooring material which has been increased by the formation of the nick grooves B, thus deteriorating the fitting property of the flooring material with respect to the uneven subfloor. As a result, a difference in level is generated at the joint of adjacent pieces of the flooring material, so that the flooring material cannot be installed with high precision and that the floor squeaks to footsteps because of the lifting up of the flooring material from the surface of the subfloor.
Conversely, if the depth of the nick groove B in the back face of the wood overlaid board A is reduced, the pieces d are integrated at their upper portion, so that the strength of the tongue D is increased. However, this lowers the flexibility of the flooring material, so that the fitting property with respect to the subfloor is deteriorated and therefore the flooring material cannot be installed with high precision, either, similarly to the foregoing case.
Moreover, since the tongue D and groove E are formed only on the side faces of the wood overlaid board A, the fitting condition between the tongue D and groove E is not excellent, so that a fitting operation in joining two pieces of the flooring material requires more labor. In the case where the wood overlaid board A is warped or distorted, the fitting operation itself may become substantially impossible.